Middle Lias (Undifferentiated) [Obsolete Name And Code]

Siltstones, sandstones, ironstones and limestones with subsidiary mudstone or sandstone.

Definition of Lower Boundary:

Base of Upper Pliensbachian or base of arenaceous/calcareous strata belonging to either Lower or Upper Pliensbachian. [See notes under "Geographical Limits".]

Definition of Upper Boundary:

Top of Upper Pliensbachian or top of arenaceous/calcareous/ferruginous strata belonging to either the Upper Pliensbachian or the Lower Toarcian. [See notes under "Geographical Limits".]

Thickness:

Unspecified

Geographical Limits:

The term Middle Lias was used as a loose term to signify the middle, arenaceous/ferruginous part of the Lower Jurassic succcession that is now known as the Lias Group. It has commonly been used to mean Upper Pliensbachian strata (ie used in a chronostratigraphical, not lithostratigraphical, sense).